1. Field of the Invention
The present invention relates to a hydraulic clamp for use in securing a fixed member such as a metallic mould, a work and the like onto a machine tool such as a press machine, a machining center and the like, and more particularly to a hydraulic clamp of the type adapted to press and secure a fixed member between a frame body of the hydraulic clamp and a clamping-member by straightly advancing the clamping-member after rotating it by means of a clamp rod.
2. Prior Art
As such a hydraulic clamp with a direct operated rotary clamping-member, there has been known the one disclosed in the Japanese Patent Laid Open Publication No. 1982-138550 previously proposed by the inventor of the present invention.
A basic construction of the conventional embodiment, as shown in FIG. 6, is as follows.
A hydraulic cylinder 112 and a rotary actuation device 113 are arranged in series in the upward and downward direction in a frame body 103 of a hydraulic clamp 102.
A clamp rod 122 is extended below a lower wall 103a of the frame body 103, adapted to be operatively raised and lowered by means of a piston 116 of the hydraulic cylinder 112 and has a clamping-member 106 fixedly secured to the lower portion of the clamp rod 122.
The rotary actuation device 113 comprises a rotary member 127 fitted to a non-rotary member 128 so as to be spirally movable, and the non-rotary member 128 is supported by the frame body 103 through a supporting portion 129. To the contrary, the rotary member 127 is interlockingly connected to the clamp rod 122 so as to be pushed up by means of an actuation force of the piston 116.
The clamping-member 106 is adapted to be changed over between an unclamping condition A of a lowered position disengaged posture X, a clamping preparation condition B of an intermediate height position engaging posture Y and a clamping condition C of a raised position engaged posture Z in order.
The clamping-member 106 is adapted to take the unclamping condition A under a lowered returned condition wherein the piston 116 is located at a lowered position.
When the piston 116 is pushed up from the aforementioned lowered position to an intermediate height position, the rotary member 127 is rotated through a spiraling engagement with the non-rotary member 128 to rotate the clamp rod 122 while being pushed up by means of an actuation force of the piston 116, so that the clamping-member 106 is changed over to the clamping preparation condition B.
When the piston 116 is pushed up from the aforementioned intermediate height position to the raised position, the rotary member 127 and the non-rotary member 128 are simultaneously pushed up by means of the actuation force of the piston 116 so as to actuate the clamping-member 106 to the clamping condition C.
In the above-mentioned basic construction, conventionally the construction of a portion for interlockingly connecting the clamp rod 122 and the rotary member 127 was as follows. That is, as shown in FIG. 6, both these component members were integrally combined by fixedly securing the lower portion of the rotary member 127 to the upper portion of the clamp rod 122.
The hydraulic clamp 102 having the above-mentioned construction is used, for example as follows.
As shown in FIG. 6, the frame body 103 of the hydraulic clamp 102 is attached to the upper surface of a flange portion 101a of a slide 101 as a fixing side member of a press machine, and an upper metallic mould D is pressed and secured to the lower surface of the flange portion 101a in an upward facing state by means of the clamping-member 106. A pressing fixing force for the upper metallic mould D is set as follows. That is, the upper metallic mould D is subjected to lateral processing reaction forces from a work and a lower metallic mould at the time of slide lowering as well as downward subjected to a downward separating reaction force from the work or the lower metallic mould and an inertial force of the upper metallic mould D at the time of slide rising. The pressing force of the hydraulic clamp 102 is so set as to prevent the upper metallic mould D from being occationally moved by means of these reaction forces.
Incidentally, in the conventional embodiment, in order to prevent the upper metallic mould D from dropping due to its own gravity in case that such an accident as lowering an oil pressure within a clamping actuation hydraulic chamber 172 is caused by an oil leakage during a stop of the press working, the piston 116 is kept being upward resiliently urged by means of a backup spring 173 corresponding to the own gravity.
But, it is apprehended that there are the following problems associated with the above-mentioned conventional construction.
When an accident of a vanishment of a pushing up actuation force of the piston 116 is caused by a breakage of a pressurized oil supply hose and so on at the time of slide rising during the press working, the clamping-member 106, the clamp rod 122 and the piston 116 are apt to be pulled down by means of the large separating reaction force downward acting on the upper metallic mould D and the downward inertial force of the upper metallic mould D.
Firstly, the clamping-member 106, the clamp rod 122 and the piston 116 lower due to the pulling down force, so that the clamping-member 106 is changed over from the clamping condition C to the clamping preparation condition B.
Then, in the case that a rotary operation force provided for the rotary member 27 by means of the aforementioned pulling down force is larger than a frictional fixing force between the abutting surfaces of the upper metallic mould D and the clamping-member 106, the rotary member 127 and the clamp rod 122 rotate relative to the non-rotary member 128, so that the clamping-member 106 is changed over from the clamping preparation condition B to the unclamping condition A. As a result, the upper metallic mould D drops from the slide 101. To the contrary, in the case that the frictional fixing force between the abutting surfaces of the upper metallic mould D and the clamping-member 106 is larger than the aforementioned rotary operation force, the rotary actuation device 113 is locked. As a result, it is apprehended that the weakest portion of a transmission system from the clamp rod 122 to the non-rotary member 128 through the rotary member 127 is broken.